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The Brewers’ pitching staff gets most of the credit for the team’s hot start, and deservedly so. Their success comes from the most obvious source: they have allowed fewer runs than any other team. In that sense, the ultimate reason for the pitching staff’s success is fairly clear.

The lineup’s offensive production has been important too (just slightly above-average, according to FanGraphs), but the reason for its success is a bit more interesting.

We certainly hear plenty about what the Brewers lineup does not do well: they don’t walk enough (tied for second-worst in the league), aren’t patient enough at the plate (worst in the league), and that their lineup of sluggers swings for the fences and just hopes for the best.

But no one yet seems to have focused on the one thing that the Brewers lineup is doing extraordinarily well, and that is hitting line drives. Through the first 12 games of the season, the Brewers have been hitting line drives at an incredible rate: 25.5%. That line drive rate is easily the best in baseball, and is nearly two standard deviations above the current league average. Which is to say, that line drive rate is absolutely nuts.

As many of you know, balls put into play tend to be divided into ground balls, fly balls, and line drives. The definitions between these categories are not always as clear as we’d like, particularly since the statistical agencies make subjective judgments about them. But, here are some simple definitions:

A ground ball is a ball that bounces almost immediately on the ground, usually first striking somewhere in the infield.

A fly ball is the opposite: hit in the air for a reasonable distance before striking a glove or the ground. Dave Studeman estimated that a ball hit off a bat with a vertical angle of more than 30 degrees is likely to be classified a fly ball.

A line drive, on the other hand, works in between. Dave estimates that line drives tend to have no more than 15 degrees of elevation off the ground. Project Scoresheet, according to Dave, also says that a line drive should travel farther horizontally than it does vertically.

Why does the type of hit matter? FanGraphs sorts their productivity this way:

Type of Hit

Productivity

Line Drive

1.26 runs / out

Fly Ball

0.13 runs / out

Ground Ball

.05 runs / out

That’s right: a line drive is almost 10 times as likely to end up in a run as a fly ball, and over 25 times more likely to generate a run than a ground ball. That’s particularly striking considering that virtually all home runs are classified as “fly balls,” meaning that line drives are generating that ridiculous level of production primarily from singles and doubles. And yet, line drives are literally an order of magnitude more effective for a lineup.

But hopefully this also makes sense. Ground balls tend to lose speed quickly and struggle to escape the infield. Fly balls can certainly land over the fence, but the vast majority of them hang up in the air and give the defender plenty of time to run over and catch them. Line drives, of course, afford fielders neither of these luxuries. They tend to be hit hard, stay close to the ground, and dive fast for the grass. Unless the defender is in virtually perfect position, line drives will hit the ground (or the fence), put the runner on base, and advance the runners already on base.

The Brewers’ extraordinary line drive hitting explains why their lineup has been reasonably productive despite relying almost entirely on their bats for that production. It also explains why their batting average on balls in play (BABIP) has been so high for much of their early-season winning streak: when your hits tend to be line drives, a lot more of them will land in play, and you can be a bit less worried about “luck” being the reason for much of your lineup’s success.

The tricky thing with line drives is figuring out how much the Brewers can sustain their line-drive hitting. The Brewers would have to be an extraordinary collection of hitters to maintain a line-drive percentage above 25%. The major league average for 2013 was 21%, and any team performing at the 95th percentile, like the Brewers, is going to struggle to stay that far above average for long. Aramis Ramirez, for example, is currently hitting almost 40% line drives, with his career average being closer to 20%. Khris Davis is hitting 43% line drives when last year he hit only about 20%. And Carlos Gomez has a career line-drive percentage of 18% and is currently hitting them at a 35% clip.

On the other hand, writing the April line drives off as a fluke is not satisfactory either. I have not seen anyone else study the staying power of line drives, so I looked at it myself. I compared each team’s April line drive rate to its end-of-year line drive rate for the last four years (120 samples), and the connection was both moderately strong and highly significant. Specifically, about a third (31%, actually) of a team’s end-of-year line drive rate was explained by its April results. So, while an April line drive rate is no guarantee of future success, it still should end up being meaningful that the Brewers are hitting so many of them. And when some of those line drives start to disappear, many of them will still end up instead being fly balls or even ground balls, some of which the speedy Brewers can beat out for hits.

In that regard, it’s worth noting that as fantastic as the Brewers have been at hitting line drives, they’ve been equally as abysmal at hitting fly balls: more than two standard deviations below the league average. So, you can probably see where this is going. The Brewers will almost certainly lose some of these line drives, but much of that should shift over to fly balls, which is where many of the Brewers’ hitters have traditionally excelled anyway. The end result will probably be a net negative for the offense, which underscores the need for Jean Segura, Ryan Braun, and Khris Davis to start becoming more consistent offensive contributors. That said, if the Brewers maintain a decent offense this year, their ability to generate line drives will almost certainly be part of that story.